What's My Soil

A field guide to the soil under your feet

Soil series profile

Rock River soil series

Rock River is a well drained soil with a sandy loam surface, mapped on 593,759 acres in 11 counties across 3 states. Hydrologic group B.

#438 by mapped area fine-loamy Ustic Calciargids (Aridisols)

Drainage class
Well drained
99% of mapped acres
Hydrologic group
B
95% of mapped acres
Typical topsoil pH
7.2
neutral · range 7.2–7.9
Mapped area
594k
acres in 11 counties, 3 states

Typical Rock River profile

Texture and pH by depth

Typical Rock River soil profile by depth 0 in 10 in 20 in 30 in 40 in 50 in 0–3 in · H1 · pH 7.2 · 15% clay Sandy loam 3–22 in · H2 · pH 7.2 · 25% clay Sandy clay loam 22–32 in · H3 · pH 8.2 · 22% clay Sandy clay loam 32–60 in · H4 · pH 8.2 · 14% clay Sandy loam
Depth to scale. More strongly shaded layers hold more clay. Horizon names are the soil survey's (A = topsoil, B = subsoil, C = parent material).
Show as a table
Typical Rock River horizons (representative values)
Depth Texture pH Clay Sand Organic matter
0–3 in (H1) Sandy loam 7.2 15% 66% 1.5%
3–22 in (H2) Sandy clay loam 7.2 25% 57% 0.75%
22–32 in (H3) Sandy clay loam 8.2 22% 60% 0.75%
32–60 in (H4) Sandy loam 8.2 14% 67% 0.75%

Representative values from the most extensive Rock River map unit (Rock River sandy loam, 3 to 12 percent slopes, survey area CO686). Other map units of this series vary within the series range.

Hands holding dark garden soil
Stock photo for illustration, not a sample of this soil series. Credit on the Sources & method page.

What this means

What Rock River soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Rock River soils is neutral: pH 7.2 (most land between 7.2 and 7.9), the range most vegetables, flowers and lawn grasses prefer.

Loamy topsoil (loam, silt loam and similar) covers 95% of mapped Rock River acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is sandy loam (67% of mapped Rock River acres).

99% of mapped Rock River acres is moderately well to excessively drained, which suits most garden plants.

For lawns and yards

Most land is in hydrologic groups B and C, where rain soaks in at a moderate pace.

For a septic system

For conventional septic absorption fields, NRCS rates 11% of the acres in mapped Rock River soils very limited, 38% somewhat limited and 50% not limited (1% not rated, such as urban land, pits or water).

Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.

Generated from the mapped numbers above using fixed rules, not a site visit. See how these notes are written.

Where Rock River soil is found

Mapped acres

Rock River is mapped in Wyoming, Colorado and Utah.

Counties with the most mapped Rock River soil
County Acres Share of county land
Moffat County, CO 107,722 3.3%
Fremont County, WY 104,761 3.1%
Carbon County, WY 103,155 2.3%
Natrona County, WY 78,558 2.3%
Albany County, WY 70,013 3.0%
Sweetwater County, WY 44,541 0.7%
Saguache County, CO 17,186 1.2%
Lincoln County, WY 15,880 0.7%
Daggett County, UT 3,584 1.8%
Uinta County, WY 3,056 0.2%
Converse County, WY 0 0.0%

Septic absorption fields

NRCS rating, share of Rock River acres

Not limited 50%
Somewhat limited 38%
Very limited 11%
Not rated 1%
Septic tank absorption field rating across mapped Rock River acres. Scale 0 to 100% of mapped land.
Show as a table
Septic tank absorption field rating across mapped Rock River acres.
CategoryShare of acres
Not limited50.3%
Somewhat limited37.9%
Very limited10.7%
Not rated1.2%

Drainage, water table and flooding

Share of Rock River acres

Depth to seasonal high water table
None reported within about 6.5 feet (median where reported).
Flooding
Not mapped as flooding on most acres.
Slope
Typically 2–9% (median 5%).
Topsoil organic matter
Median 1.5%.

Drainage class

Excessively drained 0%
Somewhat excessively drained 0%
Well drained 99%
Moderately well drained 0%
Somewhat poorly drained 0%
Poorly drained 0%
Very poorly drained 0%
Not rated 1%
Drainage class across mapped Rock River acres. Scale 0 to 100% of mapped land.
Show as a table
Drainage class across mapped Rock River acres.
CategoryShare of acres
Excessively drained0.0%
Somewhat excessively drained0.0%
Well drained98.8%
Moderately well drained0.0%
Somewhat poorly drained0.0%
Poorly drained0.0%
Very poorly drained0.0%
Not rated1.2%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%
B: moderate infiltration 95%
C: slow infiltration 4%
D: very slow infiltration (clayey, shallow or wet) 0%
A/D: D as is, A if drained 0%
B/D: D as is, B if drained 0%
C/D: D as is, C if drained 0%
Not rated 1%
Hydrologic soil group across mapped Rock River acres. Scale 0 to 100% of mapped land.
Show as a table
Hydrologic soil group across mapped Rock River acres.
CategoryShare of acres
A: fast infiltration (mostly sandy or gravelly)0.0%
B: moderate infiltration95.1%
C: slow infiltration3.7%
D: very slow infiltration (clayey, shallow or wet)0.0%
A/D: D as is, A if drained0.0%
B/D: D as is, B if drained0.0%
C/D: D as is, C if drained0.0%
Not rated1.2%

Sources & data dates

Source
USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
Data date
SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
Scope
All map unit components named Rock River (component kind "Series") in SSURGO: 593,759 acres.
Method
Shares are by mapped acres of Rock River components. The profile comes from the single largest Rock River component. Full methodology.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Rock River.